Aromatic polyamides are a well known class of polymers. They are discussed by Yen-Chen Yen in Stanford Research Institute Report No. 94 (Menlo Park, Calif.) entitled "Polyamides Other Than Nylons 6 and 66". They are also the subject of several papers given at the American Chemical Society meeting in April 1976-cf. Polymer Preprints, Vol. 17, No. 1, pp. 47-52, 53-58, 59-64, etc . . . ; and are described in numerous U.S. and foreign patents. See, for example, U.S. Pat. Nos. 3,063,966; 3,671,542; British Pat. No. 1,246,168; German Patent Application No. 1,951,077; French Pat. No. 1,199,458; and Japanese Patent Application No. 56/166,229.
Aromatic polyamides are generally high melting, high glass-transition temperature polymers; they display excellent mechanical properties and heat resistance and are noted for their very good chemical resistance. The main drawback of these materials is the fact that they are often extremely difficult to process. Thus, the polyamide (1) ##STR1## is always spun from solution. Suitable solvents are sulfuric acid (nearly anhydrous or oleum), chlorosulfonic acid, fluorosulfonic acid, or combinations of lithium chloride with phosphorus compounds such as N,N-dimethyldimethyl phosphinamide and the like; spinning may also be effected using nitrogen-containing solvents, such as, for example, N,N,N.sup.1 N.sup.1 -tetramethylurea, optionally in combination with an inorganic salt.
Better solubility characteristics are encountered with aromatic polyamides that are not wholly para-linked. Thus, high molecular weight polyamide (2) can be prepared via the ##STR2## reaction of isophthaloyl chloride with m-phenylene diamine in chloroform, in the presence of triethylamine as the acid acceptor. See Morgan, Polymer Preprints, Vol. 17, No. 1, p. 47. However, these polyamides are also very difficult to process.
Improved melt-fabricability characteristics were claimed for polyamides processing a flexibilizing oxygen bridge within their molecules. Thus, according to Japanese Patent Application No. 56/166,229 polyamides based on the diamine (3) and iso- and/or terephthaloyl chlorides ##STR3## possess good thermal stability, good electrical and mechanical properties and can be molded into useful shapes. The moldability is still poor, however; in order to improve ease of fabrication the subject polyamides were plasticized using, for example, various bisphthalimides, as described in Japanese Patent Application Nos. 59/147,046 and 59/147,047, siloxanes (see Japanese Patent Application No. 59/142,247), and the like. Also, processibility was presumably improved when the polyamides in question were blended with poly(aryl ether sulfones) such as (4) or with polyarylates such as (5). See Japanese Patent Application Nos. 58/52,348 and 58/52,347. ##STR4##
Polyimides are a well known class of polymers. They are described by Cassidy in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 18, pp. 704-719. C. Arnold, Jr., in the Journal of Polymer Science; Macromolecular Reviews, Vol. 14, pp. 265-378 (1979) devotes a portion of the article entitled: "Stability of High-Temperature Polymers", at pp. 322-333, to polyimides. They are also discussed by Elkin in Stanford Research Institute Report Number 86 (Menlo Park, CA.) entitled "High Temperature Polymers" (1973). Polyimides and amide-imides are reviewed in Cotter, et al., Ring Forming Polymerizations, Vol. B.2 pp. 1-67, Academic Press, New York, (1972). The physical and chemical characteristics of polyimides and the subclass of poly(amide-imides) have been well documented.
In general, polyimides (especially aromatic polyimides) have excellent heat resistance but are difficult to process. The same is generally true with respect to aromatic poly(amide-imides). Thus, according to P. E. Cassidy et al. (cited above), "wholly aromatic polyimide molding powders must be fabricated by sintering at high temperature and pressure". Injection molding and extrusion are thus not possible. J. M. Aducci in Polyimides, K. L. Mittal, Editor, 1984, published by Plenum Press, New York, states on page 1024:
Polyimides, produced by the chemical reaction of an aromatic dianhydride and an aromatic diamine, were the first of the aromatic thermally stable polymers introduced in the mid-1950's. Polyimides did not behave as thermoplastics even though they had linear structures. Polymer backbones comprised of rigid, inherently stable, aromatic phenylene and imide rings imparted polyimides with excellent thermal oxidative properties and at the same time made them exceedingly difficult to process because of their high and sometimes indeterminate melting points."
According to T. P. Gannett et al., in U.S. Pat. No. 4,485,140, the polyimide of the structural formula: ##STR5## where R.sub.1 and R.sub.2 are -CH.sub.3 or -CF.sub.3, is typical of aromatic polyimides which are generally infusible. According to Alberino et al., U.S. Pat. No. 3,708,458, a polyimide having recurring units of the formula: ##STR6##
"possesses highly useful structural strength properties but . . . is difficult to mold, by compression at elevated temperatures, because of its relatively poor flow properties in the mold". The patentees developed a polyimide to overcome, to some extent, these difficulties by including in the polymer backbone a certain proportion of the reaction product of 3,3',4,4'-benzophenone tetracarboxylic dianhydride with 2,4- or 2,6-toluene diamine (or the corresponding diisocyanates). The copolymers were regarded as having better flow properties in the mold even though such difficult molding procedures as "sintering or hot processing" were the criteria used.
Thus, it can be said that aromatic imide-based polymers in general do not lend themselves easily to melt fabrication except perhaps by compression molding.
Recently, the processability of some of these imide-based materials has been improved by blending or alloying them with other resins which are themselves more easily melt processable by virtue of being more easily thermoformed and injection molded.
Thus, it is desirable to prepare amide and/or imide containing polymers which would combine toughness with ease of melt fabrication without the necessity of using a monomeric and/or a polymeric additive. It is obviously also highly desirable that the novel materials retain the very good high temperature properties that are characteristic of aromatic polyamides, poly(amide-imides), and polyimides. Also, these latter resins are known for their generally undesirably high water absorption (3 to 10 wt. %, depending on the particular polymer). High water absorption affects deleteriously the dimensional and the thermal stability of a product; it reduces its mechanical property values and limits its fabrication latitude. Therefore, the preparation of an amide and/or imide containing polymer displaying a consistently low, e.g. 3 weight percent, water uptake is a very important and worthwhile goal.